Rocky Mountain iris
Iris missouriensis · Iridaceae
Rocky Mountain iris (Iris missouriensis) is a perennial herbaceous plant in the Iridaceae family. It is native to North America. USDA records it as hardy in zone 4 and warmer, down to about -28°F.
At a glance
| Type | forb-herb USDA |
|---|---|
| Lifecycle | perennial USDA |
| Native status | native USDA |
| Mature height | 1 ft USDA |
| Light | part-shade USDA |
| Water need | high USDA |
| Growth rate | rapid USDA |
| Soil pH | 7–8.5 USDA |
| Bloom | March–May USDA |
| Flower color | Purple USDA |
| Hardiness zones | 4 and warmer USDA |
| Guild layer | ground-cover Derived |
| Nursery availability | Routinely Available USDA |
USDA quoted from the USDA PLANTS database · Derived computed by a fixed rule from those columns. No value on this page is estimated.
Growing conditions
It grows in partial shade. USDA rates it as having needs consistently moist ground. Its drought tolerance is rated low. It tolerates saturated, poorly drained ground well (USDA rates its anaerobic tolerance high). It is recorded on soils from pH 7 to 8.5 — a broad range that spans acidic through mildly alkaline ground. Its cold limit is zone 4.
Size and growth
At maturity it reaches about 1 ft, making it a low, mat-forming plant. It grows quickly.
Bloom period
USDA records a bloom period of March through May. Flowers are purple.
A flowering date, not a pollinator rating.
Foliage, flower and season
Summer foliage is green, medium in texture. Its flowers are conspicuous. Its fruit or seed heads are conspicuous, extending interest past flowering. Its active growth period is summer. USDA rates its lifespan as short, so plan on replacing or resowing it rather than treating it as permanent structure.
What the site needs to provide
USDA records it across sites receiving 24 to 35 inches of annual precipitation. It needs at least 115 frost-free days to finish its season. It roots to at least 6 inches. Fertility requirement: low — no feeding needed on ordinary garden soil.
Propagating it
It takes readily from seed, bare root, bulbs and corms. USDA records no cold-stratification requirement, so seed should germinate without a chilling period. Its seed spreads at a moderate rate. It spreads vegetatively at a rapid rate.
Resilience and wildlife
Browsing animals rate it barely palatable — the sourced basis for calling it deer-resistant. Its fire tolerance is rated high. Its growth form is recorded as colonizing.
Role in a guild
Ground cover. In a layered planting this is the lowest layer — it shades soil, holds moisture, and suppresses weeds. The layer is derived by a fixed rule from growth habit and mature height.
Tags
Related plants
Others in Iris
- Siskiyou iris Iris bracteata
- copper iris Iris fulva
- toughleaf iris Iris tenax
- Virginia iris Iris virginica
Similar role and hardiness
- thrift seapink Armeria maritima
- alpine aster Aster alpinus
- Japanese pachysandra Pachysandra terminalis
- longbeak buttercup Ranunculus longirostris
- New York fern Thelypteris noveboracensis
Where this data comes from
Every value on this page comes from the USDA PLANTS database record for symbol IRMI, or is computed from those values by a fixed rule. Nothing here is estimated or model-generated. Where USDA publishes no value, this page omits the claim rather than filling the gap.
- Quoted from USDA PLANTS: active growth period, Bloom, Bloom end, browse palatability, cold stratification, Drought tolerance, fall conspicuous, fertility requirement, fire tolerance, Flower color, flower conspicuous, foliage color, foliage porosity winter, foliage texture, frost free days min, fruit conspicuous, growth form, Growth rate, Hardiness zones, Lifecycle, lifespan, Light, Mature height, Minimum temperature, Native status, Nitrogen fixation, Nursery availability, precipitation max in, precipitation min in, propagation, resprout ability, root depth in, seed spread rate, Soil pH, Soil pH (upper), Tolerance of wet soil, Toxicity, Type, vegetative spread rate, Water need.
- Derived by a fixed rule from those columns: Guild layer.
Read our full data sources and methodology.
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